The present invention relates to a method and machine for positioning films, such as color separation films used in multi-color printing, on transparent base sheets according to a desired layout.
As is well known, color printing is performed by superimposing different colored inks by employing a plurality of printing plates which are produced by separating an original picture into several colors; for example, cyan, magenta, yellow, and black.
When a printing layout includes several pictures, each picture is generally color-separated independently and color separation films of each picture are made separately. Then, the color separation films for each color are collated and mounted on a transparent base and are printed in contact with a printing plate material, such as a pre-sensitized plate to obtain an original color separation plate for printing of the desired layout.
It is essential that the various color plates print precisely in coincidence, to prevent "color mackle", which would otherwise impair the printing quality, and thus it is critical that the relative positions of the various picture, mounted on the layouts for each color, exactly correspond. Hitherto, several methods have been developed for performing the positioning operation of mounting the color separation films on the layouts, and a summary of some of these known methods is set forth hereinbelow.
In the first method, which is at present the one which is most frequently used, position lines for the original films are drawn on a backing sheet of the necessary size, according to the desired layout. A transparent base is overlaid on the backing sheet and then for one of the separation colors, the separation films for each picture are laid individually on the transparent base by adjusting registration marks on the films to coincide with marks on the backing sheet by eye and they are secured to the transparent base by adhesive tape, to obtain a first original color separation plate. This process is repeated for each color to obtain all of the original color separation plates.
By this method, however, the accuracy of the setting positions of the films depends on the skill and care of an operator and accordingly it is unstable and erratic. Furthermore, the operational speed is low.
In a second known method, the transparent bases for each color, and the original color separation films are provided with punched apertures and the positioning of the color separation films on the transparent bases is effected by inserting registering pins into the punched apertures.
In this method, for instance, when four color inks are used for printing, four transparent bases (one of each color) are put on the backing sheet and the four original color separation films of each picture are placed on the four transparent bases one by one, according to the desired layout. Then, the four transparent bases and each set of four color separation films are punched all together in a single operation, and then separated one from another. The transparent base sheets and the color separation films of each color, which are recollated, are positioned by using the register pins, as mentioned above. In practice, however, this method is prone to errors due to slippage when the eight film sheets are punched together. If, for example, the operator uses a handheld power drill for the punching operation, which is convenient in a plate-making factory, it is fairly difficult to maintain a position perpendicular to the film sheets, so errors in the alignment of the apertures in the film sheets are liable to occur. Furthermore, the operation of inserting and removing the registering pins is troublesome and time consuming.
In a third method, the positions of the register marks of the original color separation films are detected by photoelectric detector means and the original color separation films are automatically moved to the correct positions if the register marks are out of alignment, and then are provided with the punched apertures. Then, the original color separation films are laid out on a transparent base sheet which is positioned by inserting the register pins into its punched apertures, by a pinbar, having a pair of standing pins for locating the original color separation film, capable of moving upward and downward and in the X and Y directions over the setting surface of the base sheet for the color separation films. In this method, first the color separation films of one color are located in the desired positions by locating the color separation films for each picture in turn to the pinbar, and the pinbar is moved to the desired alignment on the layout. Then, the position of the color separation film is stored into a memory, and the setting operation for the color separation films of the other colors on the base sheets is repeated by utilizing the stored data in the memory. This method enables accurate positioning of the original films and is highly practicable but requires a large system and accordingly high costs are involved.
In a fourth method, as in a similar manner to the third method, first the original color separation films are automatically positioned in the correct positions and then are punched. Then, the color separation films of one color are laid out on the base sheet by locating the color separation films for each picture to a plurality of pinbars which are fixed to the desired positions during the operations. Then, the setting operation for the color separation films of the other colors on the base sheets are repeated in the same manner as described above. This method does not require a memory and enables accurate positioning of the films but again involves high cost.